Microplastics analytics: why we should not underestimate the importance of blank controls

Abstract

Recent years have seen considerable scientific attention devoted towards documenting the presence of microplastics (MPs) in environmental samples. Due to omnipresence of environmental microplastics, however, disentangling environmental MPs from sample contamination is a challenge. Hence, the environmental (collection site and laboratory) microplastics contamination of samples during processing is a reality that we must address, in order to generate reproducible and reliable data. Here we investigated published literature and have found that around 1/5 of studies failed to use blank controls in their experiments. Additionally, only 34% of the studies used a controlled air environment for their sample processing (laminar flow, fume hood, closed laboratory, clean room, etc.). In that regard, we have also shown that preparing samples in the fume hood, leads to more microplastics > 1 μm) contamination than preparing it in the laboratory bench and the laminar flow. Although it did not completely prevent microplastics contamination, the processing of sample inside the laminar flow is the best option to reduce sample contamination during processing. Overall, we showed that blank controls are a must in microplastics sample preparation, but it is often overlooked by researchers.

Supplementary information: The online version contains supplementary material available at 10.1186/s43591-023-00065-3.

Keywords: Contamination; Negative control; Procedural controls; Reliability of data; Standardization.

Fig. 1

Characterization of blank control samples processed in a laminar flow cabinet (L. flow), a fume hood (F. hood), or directly on a bench (Bench) by confocal Raman spectroscopy. Histograms of the (a) length, (b) width, and (c) area distributions of microplastic particles found to contaminate blank controls. In (d) the counts of the different plastic and non-plastic particles present in each sample are shown. In (e) the composition of only the MPs detected in the different samples are shown. In (f) the number of MPs found in a human follicular fluid MPs sample (from Grechi et al. 2023) were corrected to the different blank controls presented in (e), and to the blank control that was ran in parallel with the follicular fluid sample (Fol. Fluid). Samples were corrected to the blanks by subtracting the number of particles detected in the water blanks from the corresponding number of particles detected in the follicular fluid sample for each specific plastic polymer individually

Fig. 2

Summary of key findings related to the use of blank controls in the peer-reviewed literature. The figure displays the percentage of manuscripts that employed, demonstrated, detected, and corrected their samples using blank controls. It also showcases the percentage of manuscripts that used controlled air flow environments (laminar flow vs fume hood) for sample processing, and the size range of particles detected in the blank controls